void main(){
  //根据属性名传递可选参数(常用)
  printPerson("jack");
  printPerson("jack",gender:"male",age:21);
  printPerson("jack",gender:"male");
  //根据参数顺序传递可选参数
  printPeople("Rose");
  printPeople("Rose",20,'female');
}
//可选参数要写在参数列表的最后
printPerson(String name,{int age,String gender}){
  print('name=$name,age=$age,gender=$gender');
}
//默认参数可以直接通过等号赋值
printPeople(String name,[int age=88,String gender]){
  print('name=$name,age=$age,gender=$gender');
}
